JWST Sunscreen Offers SPF 1,000,000

The James Webb Space Telescope will have a sunshield that is about the size of a tennis court, and mission managers say it will offer the best “SPF” (Sun Protection Factor) in the Universe.

“Each of the five layers of the shield is less than half the thickness of a piece of paper,” said John Durning, Deputy Project Manager for JWST. “The five work together to create an effective SPF of 1,000,000.”

This sunshield protects the observatory from unwanted light, keeping it cool and allowing it to detect heat from faraway objects in the universe. So, how do you get something that large into orbit?
The sunshield will be folded up during launch, and then deployed in a special process that will take seven hours once the telescope reaches its destination at about 1.5 million km (1 million miles) from Earth. Two deployable towers, or Mid Boom Assemblies (MBA), will stretch the sunshield open.

The completion of this hour-long process triggers another mechanism that separates the sunshield’s five layers, readying the sunshield for work.

The video above shows how the special mechanisms for deploying the sunshield will work.

The sunshield will protect the telescope’s sensitive infrared instruments from the heat and ultraviolet radiation from the Sun.

The sunshield measures 20 meters (65.6 ft.) by 12 meters (39.3 ft.). It is made of a film-like material called Kapton, which is pliable enough that can be folded like a blanket, but strong enough to remain stable in wide range of temperatures, from 36K to 650 Kelvin (-395°F to 710°F or -237 to 377°C).

But JWST will observe primarily the infrared light from faint and very distant objects, so the telescope and its instrument must be very cold, at an operating temperature of under 50 K (-370F/-223C). If the sunshield does its job, the Optical Telescope Element and the Integrated Science Instrument Module on the telescope’s topside will stay cool enough by staying in the shade of the sunshield.

The Webb telescope will orbit 1,513,000 km (940,000 miles) from Earth at the L2 Lagrange point and is the first deployable optical telescope in space.